With the coming of blood component therapy, most whole blood collected today is separated into its clinically proven components for storage and administration. The clinically proven components of whole blood include red blood cells, used to treat chronic anemia; platelet-poor plasma, from which Clotting Factor VIII-rich cryoprecipitate can be obtained for the treatment of hemophilia; and concentrations of platelets, used to control thrombocytopenic bleeding.
In a typical conventional processing method, whole blood is first separated by centrifugation into red blood cells and platelet-rich plasma. The platelet-rich plasma is then processed into platelet concentrate and platelet-poor plasma by further centrifugation or by a separate filtration step.
FIG. 1 shows a representative prior art system 10 for processing platelet-rich plasma to obtain platelet concentrate and platelet-poor plasma by filtration. The system 10 includes a membrane separation device 12 of the type shown in copending U.S. patent application Ser. No. 052,171, filed May 5, 1987, and entitled "Blood Fractionation System and Method." The device 12 employs a rotating microporous membrane 14 to separate platelets from platelet-rich plasma. The device 12 also can be used to separate red blood cells from whole blood. The separation device 12 is also shown in FIG. 2 and will be described in greater detail later.
A separation device 12 like that described and claimed in the '171 Application is commercially sold by the Fenwal Division of Baxter Healthcare Corporation under the trademark "Plasmacell-C".TM..
As FIG. 1 shows, the separation device 12 is used in association with a processing apparatus 16. A processing apparatus like that shown in FIG. 1 is sold by the Fenwal Division of Baxter Healthcare Corporation under the trademark "Autopheresis-C".TM..
The system 10 shown in FIG. 1 can process about 600 ml to 700 ml of platelet-rich plasma in about 15 minutes. The platelet-rich plasma to be processed is typically first collected in a container 18 in a preliminary separation step, during which whole blood from a donor is centrifugally separated into red blood cells and platelet-rich plasma. The collected platelet-rich plasma is then pumped from the container 18 into the separation device 12 at a flow rate of about 50 ml/min., while the membrane is rotated at about 1600 RPM's. The platelets are separated from the platelet-rich plasma in a single pass through the separation device 12. Platelet-poor plasma is pumped into a collection container 22 at a flow rate of about 35 ml/min. The platelet concentrate flows into a collection container 20.
As used in the above manner, the separation device 12 operates at a separation efficiency of about 70%. This means that 70% of the total plasma volume contained in the platelet-rich plasma that is delivered to the device 12 is ultimately collected as platelet-poor plasma. The remaining volume (about 200 ml) is the plasma in which the platelet concentrate is suspended.
Thousands of these procedures have been successfully done using the system 10 shown in FIG. 1. Still, there remains a demand for new systems and methods that can process even larger volumes of fragile cellular rich suspension at even higher flow rates. High volume processing of cellular suspensions containing platelets pose even additional challenges, because platelets are among the most fragile and easily traumatized of the cellular constituents of blood.